We have seen a lot of counterfeits near this price point. Here is our usual disclaimer:
Here are links to our authorized dealers partners, as well as a list of non-authorized merchants:
http://www.sennheiserusa.com/serviceandsupport_dealer-locator
http://www.sennheiserusa.com/nonauthorized
Authorized dealers have a direct relationship with Sennheiser while upholding the highest standards for product integrity in the logistics chain. At any given time, a Sennheiser representative can validate the product at its current position in the supply chain.
Non-authorized dealers selling "legit" product have no relationship with Sennheiser. They may get their goods from a source that is questionable; perhaps they are stolen, returned, refurbished (even though they say they are new), new, old, counterfeit...we have no idea. They may not have been stored in the proper environment (were they in a truck for an entire winter with no heat?) and thus we cannot guarantee the product to perform as it would when going through the appropriate supply chain.
If a price is "too good to be true", it generally is. Only buy from an authorized dealer in your country.